A number of ultrasonic devices have heretofore been proposed for use in ablating or removing obstructive material from anatomical structures, such as blood vessels. Examples of devices which purportedly utilize ultrasonic energy, alone or in conjunction with other treatment modalities, to remove obstructions from anatomical structures include those described in U.S. Pat. Nos. 3,433,226 (Boyd), 3,823,717 (Pohlman, et al.), 4,808,153 (Parisi), 4,936,281 (Stasz), 3,565,062 (Kuris), 4,924,863 (Sterzer), 4,870,953 (Don Michael, et al.), 4,920,954 (Alliger, et al.), and 5,100,423 (Fearnot) as well as other patent publications WO87-05739 (Cooper), WO89-06515 (Bernstein, et al.), WO90-0130 (Sonic Needle Corp.), EP316789 (Don Michael, et al.), DE3,821,836 (Schubert) and DE2,438,648 (Pohlman).
Ultrasound transmitting catheters have been utilized to successfully ablate various types of obstructions from blood vessels of humans and animals. Particular success has been achieved in ablation of obstructions located in peripheral blood vessels such as the femoral arteries. Successful application of ultrasonic energy to smaller blood vessels, such as the coronary arteries, has also been achieved. Such applications necessitate the use of ultrasound transmitting catheters which are sufficiently small and flexible to undergo transluminal advancement through the tortuous vasculature of the aortic arch and coronary tree.
Additionally, ultrasound transmitting catheters may be utilized to deliver ultrasonic energy to blood vessel walls for the purpose of preventing or reversing vasospasm as described in copending U.S. patent application Ser. No. 07/911,651, entitled ANGIOPLASTY AND ABLATIVE DEVICES HAVING ONBOARD ULTRASOUND COMPONENTS AND DEVICES AND METHODS FOR UTILIZING ULTRASOUND TO TREAT OR PREVENT VASOSPASM.
Thus, it is apparent that the use of ultrasound therapeutic procedures provides substantial benefits. However, a problem commonly associated with the performance of such procedures is the inability to readily determine proper functioning of the ultrasound delivery system. As those skilled in the art will appreciate, the presence of the desired level of ultrasound energy at the distal end of the ultrasound catheter cannot be determined by visual inspection or feel. Thus, the operator cannot easily ascertain whether or not the ultrasound delivery system is providing the desired level of ultrasound energy at the distal end of the ultrasound catheter.
It is necessary that the ultrasound delivery system be functioning properly in order to provide the desired therapeutic effect. It is common for ultrasound delivery systems to function suboptimally or not at all due to loose mechanical connection of the ultrasound transmission member, breakage of the ultrasound transmission member, failure of the ultrasound transducer, and failure of the ultrasound generator and control electronics, as well as for various other reasons.
Various things can happen to the different components of the ultrasound delivery system during shipping, handling, and use thereof so as to cause the ultrasound delivery system to function suboptimally. For example, rough handling of the piezoelectric crystal of the ultrasound transducer can result in damage thereto which causes the system to function at less than the desired level and which is not readily apparent to the user. The piezoelectric crystal itself may become cracked or broken, or the electrical leads thereto may fail so as to provide inadequate electrical conduction. Indeed, a wide variety of different types of malfunctions and component failures may occur so as to render operation of the ultrasound delivery system suboptimal.
It is also possible for the operator to improperly set up or operate the ultrasound delivery system so as to inadvertently cause the system to operate suboptimally. For example, an inappropriate level of ultrasound vibration may inadvertently be selected by the operator, thus potentially rendering the therapeutic procedure ineffective. For example, a level of ultrasound vibration appropriate for coronary procedures may inadvertently be selected when a peripheral procedure is to be performed. The level of ultrasound vibration commonly associated with coronary procedures is substantially lower than that generally desired for use in peripheral procedures. Thus, even though a visual indication, e.g., status light or digital readout, of the selected procedure may be provided at the signal generator, it is possible for the operator to overlook such visual indication and to perform the procedure at an ultrasound energy level other than that desired.
Thus, it is possible to perform an entire therapeutic procedure with an ultrasound delivery system providing suboptimal or zero output and without the operator being aware of such problem. Contemporary methodology provides no means for assuring proper operation of the ultrasound delivery system during therapeutic procedures.
The performance of such therapeutic procedures with an ultrasound delivery system providing suboptimal or no ultrasound energy has potentially serious consequences for the patient. For example, rather than ablating the material comprising a stenosis, the distal end of the catheter may undesirably dislodge portions thereof or may compact the stenotic material against the vessel walls. Such breaking away of stenotic material or compaction thereof may go unnoticed until a serious problem caused thereby arises. Stenotic debris may potentially form an embolism, thus impeding the flow of blood to a vital organ, e.g., the brain. Compaction of stenotic material may provide a base upon which further stenotic material may subsequently accumulate.
As such, it would be beneficial to verify proper operation of the ultrasound delivery system prior to commencing the therapeutic procedure for which the ultrasound delivery system is to be utilized.